From a control-engineering standpoint the terms \(\eta _x\)  and \(\eta _y\)  should be related to actuators faults. Introduce therefore the two “decoupled” ultra-local models ([1]}, [2]}):
\(\dot{z}_x = F_x + \alpha _x u_{\rm MFC}, \ \dot{z}_y = F_y + \alpha _y v_{\rm MFC}\) 
